An electron moving with velocity v → = i ^ v x enters a uniform magnetic field B → = k ^ B z . The electron experiences

a force but its kinetic energy does not change.

a force and its kinetic energy decreases.

a force and its kinetic energy increases.

no force hence kinetic energy does not change.

A loop of flexible wire of irregular shape carrying current is placed in an external magnetic field. Identify the effect of the field on the wire.

Loop assumes circular shape with its plane normal to the field.

Loop assumes circular shape with its plane parallel to the field.

Wire gets stretched to become straight.

Shape of the loop remains unchanged.

E M B I B E

Physics Crash Course BITSAT>Chapter 14 - Magnetic Effect of Current>Exercise 1>Q 41

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IMPORTANT

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Assertion : Two charged particles are released from rest in gravity free space. After some time, one particle will exert a non-zero electrostatic force on the other particle.

Reason : A moving charge cannot produce magnetic field. But a magnetic force may act on a charged particle moving in an external magnetic field.

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Important Questions on Magnetic Effect of Current

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IMPORTANT

Physics Crash Course BITSAT>Chapter 14 - Magnetic Effect of Current>Exercise 1>Q 42

Assertion : The density of field lines decreases in a medium of high permeability

Reason : Because $B \propto \frac{1}{μ}$

MEDIUM

Physics

IMPORTANT

Physics Crash Course BITSAT>Chapter 14 - Magnetic Effect of Current>Exercise 1>Q 43

Charge

q

is uniformly spread on a thin ring of radius

R

. The ring rotates about its axis with a uniform frequency

f Hz

. The magnitude of magnetic induction at the centre of the ring is

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Physics Crash Course BITSAT>Chapter 14 - Magnetic Effect of Current>Exercise 1>Q 44

An electron moving in a circular orbit of radius $r$ makes $n$ rotations per second. The magnetic field produced at the center has a magnitude,

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Physics

IMPORTANT

Physics Crash Course BITSAT>Chapter 14 - Magnetic Effect of Current>Exercise 1>Q 45

A charge

Q

is uniformly distributed over the surface of non-conducting disc of radius

R

. The disc rotates about an axis perpendicular to its plane and passing through its centre with an angular velocity

ω

. Aš a result of this rotation a magnetic field of induction

B

is obtained at the centre of the disc. if we keep both the amount of charge placed on the disc and its angular velocity to be constant and vary the radius of the disc then the variation of the magnetic induction at the centre of the disc will be represented by the figure :

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Physics Crash Course BITSAT>Chapter 14 - Magnetic Effect of Current>Exercise 1>Q 46

Using mass

(M)

, length

(L)

, time

(T)

and current

(A)

as fundamental quantities, the dimension of permeability is:

HARD

Physics

IMPORTANT

Physics Crash Course BITSAT>Chapter 14 - Magnetic Effect of Current>Exercise 1>Q 47

All straight wires are very long. Both $A B$ and $C D$ arcs of the same circle, both subtending right angles at the centre $O$ . Then the magnetic field at $O$ is-

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Physics Crash Course BITSAT>Chapter 14 - Magnetic Effect of Current>Exercise 1>Q 48

Identical currents flow in two perpendicular wires, as shown in the figure. The wires are very close but do not touch. The magnetic field can be zero:

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